Actuating apparatus for sound system



April 22, 1952 P. L. KARR ACTUATING APPARATUS FOR SOUND SYSTEM 2 SI-IEETS--SHEET 1 Filed March 5, 1948 April 22, 1952 p KARR 2,594,178

ACTUATING APPARATUS FOR SOUND SYSTEM Filed March 5, 1948 2 SHEETS-SHEET 2 Patented Apr. 22, 1952 FFECE ACT U ATI'NG APPARATUS For: SOUND SYSTEM Philip L. -.Karr,. Cliica'go, Ill-., assignor to Excel MovieProducts, Inc., a corporation of Illinois ApplicationMai-chfi, 1943, Serial No. 13,245

This invention relates to a sound system and more particularly to actuating apparatus for a sound system,

One feature of this invention is that it provides improved means for substantially eliminating hum in asound system whichisenergized by a varying current; another feature of thi inventicn is that it provides a sourceof actuating Waves comprising a wave emitting member which is heated to a radiant temperature, but not to ex ceed a temperature of the orderof about 1800 Fahrenheit; a further feature of this invention is that it provides a source of actuating waves-of relatively long wave length emitted by a member heated not to exceed a temperature wher'e it is characterized by a red or red-orange light; an additional feature of this invention is that'it provides a source of actuating Waves comprising a wave emitting member which operates in open air and which is heated to a radiant temperature too low to cause deleterious oxidation; still' another feature of this invention is that it provides a source of actuating waves comprising a waveemitting member which emits waves substantially entirely within a narrow band o'mprisingonly' a small portion of the lower end of the radiant energy frequency range; yet' a" further feature of this invention is that it provides a"re1ative1y low voltage wave emitting member coupled to a relatively high voltage circuit already in the system; still another feature of this invention isthat it provides improved apparatus for developing ac tuating waves, including means for reaauyre mov'ably positioning the wave'einitting member and means providing automatic connection of Fig. 2 is an enlarged fragmentaryverticalsection through a portion'o'ttlie projector shown' in Fig. 1;

Fig. 3 is a fragmentary verticalsection along the line 3-3 of Fig. 2;

Fig. 4 is a detail plan view of' a portionofthe apparatus of Fig. 3; r

Fig. 5 is a schematic diagram of a portion of the operating circuit of the projector; and

Fig. 6 is a schematicdiagr'am 'showing'a modified form of operating circuit'.

Whileit will be apparent to thoseskilledain the art that the invention disclosedi'nthis 'speci-' 14 claims. (01. 179-1003) ficat'ion is applicable to many different types of sound systems, the invention is illustrated as applied to a motion picture sound projector, and the invention will be described in connection with such a projector.

In the projector illustrated in Fig. 1 a casing 10 carries a film feed spool I i and a film take-up spool [2, at least the take-up spool being driven in conventional manner as by an electric motor in the housing and not visible in Fig. 1 (see 43 in Fig. 6). A film l3 which is initially wound on the feed spool H is transferred to the take-up spool (-2 during the operation of the projector, this film passing oved a sprocket l4, and from where it is fed'past a film gate :5 which may be convention A projector lamp (see 40 in Fig. 5) within the casing iii illuminates that portion of the film which is opposite the aperture in the gate l5, and a lens arrangement I6 is adapted to focus the beam of light .on a screen.

As is Well understood in the art, means are provided for causing, the film to move intermittently pastlthe gate so that each frame is stationary during the time that light from the projector lamp, is thrown upon it. This means is illustrated as comprising the claw driven in conventional manner by the cam arrangement 5 5. After leaving the gate l5 the film passes over a roller Ll, being held in frictional contact with said rollor by a lever arm l8 and supplemental roller Ida. A sound drum 19 carries the now continuously moving film past the sound take-off apparatus, andthe film then moves over another roller 25, ovei" a take-up sprocket 2 I, and on to the talze-up spool l2. The general operation of the apparatus just described is conventional and will not be further described here. i

As is conventional, the film l3 carries (usually along one edge) a sound track l3a, and a source of actuating waves are provided, these waves being modulated by the sound track and reproduced in any conventional manner, as for example by an amplifier and speaker arrangement associated with the projector. In a projector being built and incorporating the inventions here being claimed the audio Waves are caused to modulate radio frequencies and these are transmitted to a separateamplifying and reproducing system, as for example that ofa conventional radio receiver.

Inthe conventional sound projector provided with a Source of radiant energy on one side of the sound track and a translating device, as for example, a photoelectric cell, on the other side of thejsound track, the waves from the source are modulatedby the sound track on the film and the art) emits a great proportion of its radiant energy in the form of yellow and blue light waves, all of this energy being of relatively short wave lengths, and the emission of these shorter wave lengths varies tremendously with relatively on the projector adjacent the sound drum [9. At the end near the sound drum this housing is flared into a semi-cylindrical shield a which protects the photosensitive pickup device 26 from extraneous light sources. As may be seen in Fig. 3 this photosensitive pickup device extends within the sound drum l9 so that a portion of the device isadjacent the sound track [3a on the film l3. A lens 27 is mounted in a bracket 28 Within the housing 25, this bracket being yieldable to permit slight movements of the lens as a function of the position of a focusing screw 28a. The lens may comprise 'merely' a small cylindrical glass rod, preferably having a diameter about A; of an .inch. At the end of the housing remote from the sound'drum there is an opening closed by a threaded cap 29, and within this opening and small changes in temperature of the lamp filament. For example, in a tungsten filament which is heated below incandescence and only to the point where it emits a dull light, a change in temperature in the filament of 200 Kelvin, as from 1000 to l200, results in a change of bright ness (measured in candles per square centimeter of filament surface) of only .005 foot candles. However, if the filament is heated to a trueincandescent point where it is glowing with a bright yellow, blue or white light, a change of 200 Kelvin, as from 3000 to 3200, results in a change of brightness of approximately 900 foot candles per square centimeter of filament surface.

If the exciter lamp is energized from a source of varying current, as for example from a conventional 60 cycle alternating current source, the filament temperature is constantly being increased or decreased at the rate of 120 cycles per second. While the filament may maintain enough brightness that this change is not noticeable to the eye, actually the intensity of the illumination emitted by an exciter lamp so energized would vary at a frequency of 120 cycles per second, and in an amount in the order of 10%, which in effect modulates thezactuating Waves emittedby the lamp with a 120 cycle signal so that a corresponding hum, sometimes termed a 60 cycle hum by virtue of the frequency ofthe current causing it, is present in the sound output.

In commercial apparatus various efforts to correct this undesirable condition have been made. For example, many projectors are equipped with means for providing a high frequency voltage to energize the exciter lamp. With this arrangement, even though the actuating waves vary at the frequency of the energizing voltage, if this frequency is above the audible range the variation is not noticeable in the sound output. Relatively complicated sharply tuned rejection circuits have sometimes been employed in the amplifiers blocking frequencies at and closely ad jacent to 120 cycles per second while passing all other frequencies. It is also possible to provide a D. C. source, as for example a battery, to energize the lamp, and this has sometimes been done. Each of these methods of minimizing hum requires the addition of expensive and bulky apparatus to the projector.

The present invention provides an extremel effective and simple way to eliminate hum from the sound output. In addition the invention provides a source of actuating waves which is considerably less complex than all sources heretofore known, is cheap and which improves the operation of the projector.

The sound take-oil apparatus of the projector is illustrated in Fig. 2. A housing 25 is mounted extending transverse of the housing is a trackway 30.

Instead of an incandescent lamp the invention provides, a wave emitting member 3| which is illustrated as a segment of Nichrome resistance wire about inch long and having a diameter of about .012 inch. This wire is secured at its respective ends to a pair of spring clips 32 which are carried on a mounting bracket 33. The bracket-33 is slidable in the trackway 30, and springs 34 on the bracket 33 are adapted to engage the trackway 30 to hold the bracket in proper position. -The spring clips 32 are biased away from each other and act to maintain the wire 3| taut and straight despite changes in the length of the wire due to temperature changes, as more fully disclosed in the application of Percy H. Case, Philip L. Karr, andHenry J. Koeber, filed June 21, 1948, as Serial No. 34,194, new Patent No. 2,545,941, granted March 20, 1951. A pair of terminals 35 are on the bracket 33, said bracket being made of insulating material. Each terminal extends through the bracket from its underside and makescontact with one of the spring clips 32, said spring clips being of conducting material. A complementary pair of terminals 316 are on the trackway 30 so that when the mounting bracket 33 is slid into the trackway the wave emitting member 3| is automatically connected into itsoperating circuit, leads 37 extending from the terminals 36 to the operating circuit.

The wave emitting member 3| is adapted to operate at relatively low voltage when compared to the projector lamp 40 or the motor 43, and said member may be energized by coupling said meme her into the circuit which provides power to operate the projector. Preferably this is accomplished by connecting the wave emitting member in series with a high impedance which is already in the sound system. For example in Fig. 5, which is the preferred embodiment, the projector lamp 40 is shown connected in a circuit comprising leads 4| and 42 which provide power to operate the system and which may be connected to a source of current, usually conventional commercial volt alternating current. The projector lamp is conventional in such a projector and is housed Within the casing [0 in such a position that its filament is behind the gate IS. The lamp 40 may be a 110 volt, 500 watt projector lamp having a relatively high impedance, practically entirely resistive. conventionally projector lamps are constructed with a tungsten filament, this material having a positive temperature-resistance co-eflicient so that as the temperature of the filament is raised its resistance is also raised with the result that, while the voltage assigns applied across the lamp from the alternating current source may be purely sinusoidal, the current is not a pure sine wave, but is fiattenedattitspositive and negative peaks.

In accordance with the preferred construction the wave emitting member 31 is connected in series with the high impedance projector lamp. Since the wave emitting member has a relatively large diameter and a short length, its resistance is Very small--less than one ohm if the member is constructed of Nichrome wire. Consequently the series connection shown in Fig. .5 will have a negligible effect upon the operation of the projector lamp, while the projector lamp will :act as a current limiting device to'protect'the member 31. Furthermore, since the resistance of the projector lamp filament increases as its temperature increases the current variations in the series circuit including the member 3| are minimized. This alone reduces the potential hum several decibels.

In Fig. 5 a modified arrangement is illustrated wherein the wave emitting member is connected in series with a different high impedance which is already in the sound system, In Fig. 6 the reference character 43 designates the motor which is utilized to drive the shutter, the sprockets, the claw and any other film moving apparatus. The motor is schematically illustrated as comprising an armature 530i and a shunt wound field 43b. Obviously many othertypes of motor may be used, shaded pole motors often being used in sound projectors. In Fig. 6 the motor isconnected'to a source of operating power by-meansof the leads Ma and A265, and the wave emitting member 3| is connected in series with the field winding 43b. In both Figs. 5 and 6 the wave emiting member operates at a relatively low voltage when compared to the lamp and motorand the impedance of the wave emitting member 3! is relatively low as compared with the current limitingimpedance' in series therewith (the lamp 4 in Fig. 5 and the motor field winding 43b in Fig. 6), and in both these modifications the impedance of the operating member is many times the'impedanceofthe wave emitting member. If desired instead of connecting the wave emitting member in series with an operating member already in the system, the wave emitting member may be coupled to the circuit which provides power for the systemby means of a small supplemental winding magnetically coupled to one ofthe motor windings to provide low voltage to energize the member 3|. In any event the circuit is arranged so that atleast a portion of the wave emitting member '3l is heated only to a radiant temperature preferably of the order of 1500" F. and not in excess of 1800" or 1856" F. For example, the member 31 may be heated so that it is characterized by a dull red or even a red-orange glow; but should not exceed this temperature in the system here being illustrated.

With a wave emitting memberv having dimensions of the order of the member 31 and mounted in metallic spring clips 32 as illustrated I have found that the spring clips dissipate considerable heat so that the ends of the waveemitting member are cooler than its center portion. For preferred operation with a Nichrom-e wave emitting member the center of the N-ichrome member reaches a maximum temperature notin excess of l800-1850 F. at and on eachside'ofthe center there is an active-or radiant-energy emitting portion, whilenear each endthe temperature isso low that there is little or no visible glow and little or no radiant energy emitted.

The advantages obtained by operating the wave emitting member at such a temperature are novel and revolutionary in the art. In the first place. when heated to such a temperature the wave emitting member emits waves in the relatively narrow infra-red and red band comprising only a small portion of the radiant energy frequency range near the lower end of said radiant energy frequency range. This band comprises frequencies having its energy content almost entirely in wave lengths of the order of 8000 angstrom units and over, and covers the relatively long wave length visible waves and the even longer wave length infra-red waves. Changes in the intensity of these waves as a result of tempera, ture changes is only very small when compared to changes in intensity in the relatively short yellow, blue, and white waves. Consequently the wave emitting member may be energized directly from varying current, as for example 60 cycle commercial alternating current, and the small variations in intensity of the emitted waves due to the cyclical temperature changes in the.memher 3| will be so small that hum in the sound output is substantially entirely eliminated. Therefore, the invention eliminates entirelythe need for converting the energizing current to a frequency above the audible range, or for 1sttempting to filter out the undesired waves.

A further advantage of the invention is that the wave emitting member may be operated in open air and need not be encased in aglass envelope or other protective device. Since the brilliant illumination (or indeed any visible light formerly required as a source of actuating waves is no longer necessary the wave emitting member may be operated at a temperature too low to cause deleterious oxidation. If a Nichrome wave emitting member of the character described is operated at a temperature of the order of 1200 no deleterious oxidation takes place and the wave emitting member will operate in open air for a great length of time. After a number of hour of operation the member 3| may become oxidized on its surface, but this relatively slow oxidation has no deleterious effect uponthe operation.

In addition, since the wave emitting member does not glow with a yellow, blue, or white light, the waves emitted are substantially entirely within a narrow band and are not spread out over the entire radiant spectrum. Consequently a very sharp image of the straight wave emitting member may be formed on the film without using a complex and expensive optical system. In the invention as illustrated the lens comprises a simple commercially obtainable glass rod having a diameter of A; of an inch. This simple lens gives a 12 to 1 reduction image so that, using a wave emitting member having a diameter of the order of .012 of an inch and spaced a substantial distance from the lens (preferably of the order of at least ten times the diameter of the lens) the actual image on the film, located'at the focus of the lens, may be less than .001 of an inch in width. Since the film moves over the sounddrum at a fixed speed the image on the film must be sharp enough that the modulation indications on the sound track do not overlap on the image at the highest frequency which it is desired-to reproduce. With the apparatus illustrated and i described here it is possible to reproduce-with clarity frequencies of the orderof 7.000 cycles per second. If the waves emitted by the member 3| covered. the entire radiant energy spectrum such asimple lens as that shown at 21 could not focus waves from the entire spectrum down to produce an image which may be less than .001 in width, and "a more expensive and more complex lens system would have to be used.

Satisfactory use of this extremely simple optical system is also facilitated by the fact that a lead sulphide cell is used which is extremely sensitive to waves in the infra-red portion of the spectrum, of the order of twenty or thirty times more sensitive to these waves than the cesium cellusually used in sound reproduction in the motion picture field. This sensitivity enables the the spirit and scope of the invention as disclosed in the appended claims.

I claim:

i. In a sound system, a source of actuating waves comprising: a wave emitting member; a

circuit for connecting said member to a varying current source; and means connecting said member into said circuit, the connection being such that said member is heated solely with said ourrent, said circuit including means for limiting the current flow through said member to a value at which said member is heated to a relatively low radiant temperature at which the hottest portion of said member glows with a redeorange light.

2. In a sound reproducing system: a metallic wave emitting member; a circuit connected to said member for connecting said member to an alternating current source for heating said member to bring the hottest portion thereof to a radiant temperature not in excess of about 1800 F. to cause at least the hottestportion of said member to glow with a dull light; a'simple cylindrical lens in the path of waves emitted by said member and spaced therefrom a distance of the order of at least ten times the diameter of .the lens; a film for modulating said waves, the film being located at the focus of the lens; and a pickup cell extremely sensitive to waves in the infrared portion of the spectrum.

3. In a sound reproducing system, a source of actuating wave comprising: an exposed Nichrome wave emitting member mounted in open air, said member having stable wave emitting-versustemperature characteristics; a circuit including said member for connecting said member to a source of alternating current for heating said member to bring the hottest portion thereof to a radiant temperature of the order of about 1800 F., said temperature being too low to cause deleterious oxidation in said member but causing at least the hottest portion of said member to glow with a dull light; and apparatus for modulating waves emitted by said member.

4. In a sound system, a source of actuating waves comprising: a wave emitting member; apparatus connected to said'member for heating said member to a relatively low radiant temperature to cause said member to emit waves substantially entirely within a narrow band compris ing 'onlya portion of the radiant energy frequency range; and one simple cylindrical lens for focusing said waves into a sharp image and comprising the only lens used.

5. Apparatus of the character claimed in claim 4, wherein said narrow band comprises frequencies having wave lengths of the order of 8000 angstrom units and over.

6. In a sound system, a source of actuating waves comprising: an exposed wave emitting member mounted in open air; a circuit including said member for connecting said member to a source of alternating current for heating said member to bring the hottest portion thereof to a temperature not in excess of about 1800 F., said temperature being too low to cause deleterious oxidation, but at least radiant to cause said filament to emit waves substantially entirely within a narrow band comprising only a small portion of the lower end of the radiant energy frequency range; and one cylindrical lens for focusing said waves into a sharp image.

7. In a sound system, apparatus of the character described, comprising: a circuit for providing power to operate said system; an operating member in said circuit, said member having relatively high impedance; and a wave emitting member connected in series with said operating member, said wave emitting member having relatively low impedancejsaid member being heated in its hottest portion to a radiant temperature of the order of 1800 F'. by current in said circuit.

8. Apparatus of the character claimed in claim 7, wherein the impedance of said operating member is many times the impedance of said wave emitting member.

9. In a sound projector, apparatus of the character described comprising: a circuit for providing power to operate said projector; an operating member in said circuit, said member having relatively high impedance; and a wave emitting member connected in series with said operating member, said wave emitting member comprising, a short, straight, large diameter metallic resistance wire, the impedance of said operating member being many times the resistance of said wire, said wire being heated in its hottest portion to a radiant temperature below incandescence and of the order of 1860 F. by current flowing in said circuit.

. 10. In a sound projector, apparatus of the character described, comprising: a projector lamp having a filament of relatively high'impedance; awave emitting member having an impedance much lower than the impedance of said filament connected in series with said filament; and means 1for focusinglight waves emitted by said projector amp.

,11. In a sound film projector, apparatus of the character described, comprising: a projector lamp havinga filament of relatively high impe dance, said lamp providing illumination for the film; a wave emitting member of relatively low impedance connected in series with said filament, said member comprising a short, large diameter resistance wire, the impedance of said operating member being many times the impedance of said member; and means for focusing light waves emitted by said projector lamp. a 12. In a sound projector, apparatus of the character described comprising: a circuit for providing power to operate said projector from a source of alternating current; a projector lamp prcviding'a light source for projection and hav? ing a filament of relatively high resistance in said circuit, said filament being constructed of material having a positive temperature-resistance coefficient; a wave emitting member connected in series with said filament, said wave emitting member comprising a large diameter wire, the resistance of said lamp filament being many times the resistance of said wire, and the temperature-resistance coeificient of said filament acting to minimize variation of current through said wire; and means for focusing light waves emitted by said lamp.

13. In a sound projector, apparatus of the character described, comprising: a motor for driving said projector; a wave emitting member connected in series with the field winding of said motor, said wave emitting member comprising a, large diameter resistance wire, the impedance of said field winding being many times the resistance of said wire; and a circuit adapted to be connected to a source of alternating current for heating said member to a radiant temperature below incandescence, at least the hottest portion of said member being characterized by a red glow when heatedto said temperature.

14. In a projector having sound reproducing means, apparatus for developing actuating waves comprising: a wave emitting member comprising a short, straight Nichrome wire; a circuit for heating said member; a bracket for mounting said member; a housing having an HILIP L. KARE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Number Name Date Hart Sept. 8, 1925 Greibach Jan. 5, 1932 Brittain July 26, 1932 Barkey Sept. 12, 1933 Six Sept. 11, 1934 Fritze Mar. 19, 1935 Lackoff et a1 June 22, 1943 Stark Nov. 2'7, 1945 Belar Apr. 27, 1948 FOREIGN PATENTS Country Date Great Britain Sept. 9, 1938 

